The present invention relates to an inflatable seat belt apparatus, more particularly to an inflatable seat belt wherein a webbing of a seat belt apparatus to restrain an occupant has an inflatable structural portion formed in an envelope shape which is usually maintained in a band shape and is inflated, in an accident in a predetermined form to withstand high temperature gas spouted from a gas generating means.
Presently, a seat belt apparatus is necessary for a vehicle or the like as an apparatus for securing an occupant's body, which restrains the occupant from sudden movement by a deceleration and an impact in a crash.
Such a seat belt apparatus comprises a webbing as a woven belt made of a fabric which has approximately a 50 mm width and is formed according to Japanese Industrial Standard, a retractor (hereinafter referred to ELR: Emergency Locking Retractor), a buckle, a tongue, an anchor and so on. The ELR winds the webbing by a winding force of a spring and locks the webbing from withdrawing only at a crash so as to restrain the occupant. The buckle is mounted on a suitable position near the floor so that the webbing fits the occupant's body well.
Conventionally, the seat belt apparatus locks the webbing from withdrawing by the function of ELR at a crash to restrain the occupant from a forward movement.
For improvement in the efficiency of restraining the occupant, each of U.S. Pat. Nos. 3,841,645, 3,865,398, and 3,866,940 discloses a seat belt apparatus in which the webbing has a portion formed in an envelope shape made of a fabric. The portion is folded like bellows and is banded by a weak adhesive so as to usually maintain in a band shape, or the portion is folded in the band shape by fastening means such as a fastener, so that, in a crash, the portion formed in the envelope shape is inflated and deployed by a spouted gas from a gas generator connected to the webbing.
According to the seat belt apparatus having the inflatable structural portion formed in an envelope shape (hereinafter, it is called as "an inflatable seat belt apparatus"), force applied to the occupant can be distributed over the range wider than the conventional webbing so as to decrease the stress applied to the occupant and a higher safety efficiency can be provided.
The inflatable seat belt apparatus is effective even for a rear seat. For mounting an air bag apparatus for an occupant on the rear seat, the air bag apparatus is generally mounted on the rear side of the back portion of the front seat. It is necessary that the front seat structure has a high rigidity for suitably operating the air bag apparatus for the rear seat to efficiently restrain and secure the occupant. However, it is difficult to provide a reclining function having a movable portion to the front seat if the air bag apparatus is mounted on the rear side of the back portion of the front seat. Therefore, the inflatable seat belt apparatus is quite effective for the rear seat because the inflatable seat belt apparatus can be independently mounted on the rear seat and has no restriction such as the air bag apparatus.
In the inflatable seat belt apparatus mentioned above, the gas generator operates according to an operation signal from a sensing unit such as an acceleration sensor sensing an impact at a crash and the envelope shape inflatable portion is then substantially instantaneously inflated and deployed in a predetermined form.
Because it is necessary to immediately spout a gas to the inflatable portion similar to the air bag apparatus, the gas generator may be a device for generating a compressed gas or compressed air filled in a compression container such as a cylinder. The compressed gas may be nitrogen or carbon dioxide gas. In case of using the compressed air, a small compressor is generally mounted.
The inflatable portion of the inflatable seat belt apparatus has a capacity which is about 1/6-1/7 of the air bag apparatus. Further, the cylinder or the like which is smaller than the air bag apparatus is enough for the inflatable seat belt apparatus.
However, the inflatable seat belt is necessary to be equipped with a device for attaching and detaching the cylinder and a device for preventing the gas from leaking. The gas pressure should be inspected periodically.
Recently, the most air bag apparatus has the gas generator (hereinafter, we call "inflator") which is a device for instantaneously generating a gas by using a rapid combustion of a compound.
The inflator receives, first, an operational signal from the acceleration sensor at a crash to act as a trigger for the electrical squib, and activates an igniter by an electrical squib; Then, a propellant burns to rapidly generate gas.
The propellant may be sodium azide (NAN3) which is well known as a propellant and generates nitrogen gas by combustion.
In the conventional inflatable seat belt apparatus, a thick fabric is folded, and the inside of the fabric is coated with silicone rubber to provide high airtightness for the envelope shape portion. Also, the inflator is provided with a simple filter for cooling the inside thereof to lower the temperature of the introduction gas, so that the high temperature gas from the inflator is directly introduced into the envelope shape portion.
The applicant has already disclosed an invention of the inflatable seat belt apparatus, wherein the envelope shape portion is formed from a knitted textile and has an inflatable unit mode of a rubber tube and situated inside thereof (Japanese Patent Applications No. 210353/1992, No. 210355/1992). Furthermore, the applicant has already disclosed an invention of the inflatable seat belt apparatus, wherein the envelope shape portion is formed from a fabric having expandable wefts and has an inflatable unit made of a rubber tube and situated inside thereof (Japanese Patent Application No. 78623/1993).
According to the above mentioned inventions, when the occupant wears the inflatable seat belt apparatus, the envelope shape portion is maintained in a thin band shape as compared with the conventional inflatable seat belt apparatus in which the thick fabric is folded. Furthermore, in an emergency, the envelope shape portion can be quickly inflated and deployed without fail.
FIG. 1 (a) illustrates an example of the inflatable seat belt apparatus, wherein a shoulder belt is formed of a knitted textile and has an inflatable unit made of rubber tube and situated inside thereof.
In this figure, numeral 51 designates a tongue. The tongue 51 has a gas inlet 54 as an inlet for introducing the gas into a rubber tube 53 arranged in the belt 52. The gas inlet 54 is coupled to a gas outlet 56a of gas generating means (inflator) 56 situated inside a buckle 55 when the tongue 51 is engaged with the buckle 55 for fixing a belt end 52a.
FIG. 1 (b) exemplifies a state of a belt 52 inflated and deployed in a predetermined form. The propellant in the inflator 56 is burned to generate a reacted gas, and the gas is introduced into the rubber tube 53 of the belt 52 through the gas inlet 54, so that the belt is inflated and deployed in the predetermined form.
As the gas is rapidly introduced into the rubber tube 53, the rubber tube is inflated as shown in the FIG. 1 (b). The shape of the whole inflatable portion is controlled by a knitted textile structure 57 formed in an envelope shape which covers the rubber tube 53. The inflatable portion has a spindle shape. Because the area of the belt portion touching the chest and the like of the occupant is increased, an impact applied to the occupant is soften.
Because the inflatable portion formed in the envelope shape is radially increased, the length of the belt in a longitudinal direction is shortened by .DELTA.L. Therefore, the inflatable seat belt apparatus has a function as a pre-tensioner which holds the occupant more effectively.
In the inflatable seat belt apparatus of this kind, the gas spouted from the inflator is introduced into the tube with a high temperature and high pressure condition as soon as the gas is generated.
FIG. 2 is a temperature distribution diagram exemplifying a result of the temperature distribution within the tube at this stage. The figure also shows the inflatable portion in an inflated condition to indicate the relative position.
At this stage, the inside of the tube has a highest temperature at a tongue portion near the gas inlet as shown in FIG. 2. In the longitudinal direction L, respective temperatures appear with introduction of the gas as shown by the dotted lines. The solid line shows a curve tracing the respective temperatures.
The gas generated by the combustion in the inflator has quite high temperature. However, because the temperature drops along the longitudinal direction, the tube works efficiently if it can withstand the high temperature only for a very short period.
Silicone rubber with a heat resistance has been adapted to the tube for receiving the high temperature gas to withstand the high temperature in the tube.
However, many cinders are produced by the combustion of the propellant of the inflator. The cinder is mainly fine carbon powder. The cinders are spouted into the tube with the reaction gas.
Because the cinder has a high temperature and has a large heat capacity compared with the gas, the cinder harms the rubber surface of the tube when the cinder collides with the inner surface of the tube. When the rubber surface is badly harmed, there is a possibility of making a hole in the tube.